1. Field
Embodiments relate to a semiconductor device and associated methods.
2. Description of the Related Art
A gate structure of metal oxide semiconductor (MOS) transistors having a minimum critical dimension of less than about 45 nm is being actively researched. The gate structure may include a stacked structure of a high-k dielectric/metal gate electrode or a stacked structure of a high-k dielectric/polysilicon gate electrode. The stacked structure of the high-k dielectric/metal gate electrode may have a threshold voltage (Vth) lower than that of the stacked structure of the high-k dielectric/polysilicon gate electrode. However, to achieve a high performance operation of transistors, the stacked structure of the high-k dielectric/metal gate electrode should have a lower threshold voltage (Vth).